Oblique-Light Illumination
Definition
Illumination of a document surface at a very low angle (5-20 degrees) to create disproportionately long shadows from surface irregularities, revealing mechanical erasure disruption, indented writing, and correction-tape edges.
Related terms
- ENFSI Document and Handwriting Working Group
- The European Network of Forensic Science Institutes working group responsible for harmonising best-practice guidelines for forensic document examination across European national laboratories.
- Foster+Freeman VSC8000
- The current-generation forensic document examination workstation produced by Foster+Freeman Ltd (UK), used by the FBI Laboratory, DSTL (UK), CFSL (India), AFP (Australia),...
- IR-Cut Filter
- A filter placed in the camera optical path that blocks near-infrared radiation, allowing only visible-range light to reach the sensor; must be...
- IR Luminescence
- Emission of near-infrared radiation by ink dye molecules when excited by visible light; different ink formulations luminesce at different intensities, allowing differentiation...
- IR Transmission
- Examination of a document with infrared radiation transmitted from below; exploits the IR-transparency of titanium dioxide in correction fluid to image underlying...
- Optical Brightening Agent (OBA)
- A fluorescent compound added to paper pulp or coatings that absorbs UV-A radiation and re-emits it as visible blue light, making paper...
- Transmitted-Light Examination
- Examination of a document with diffuse illumination from below, making paper thickness variation, watermarks, erasure thinning, and some obliterations visible as brightness...
- Video Spectral Comparator (VSC)
- A multispectral imaging instrument combining UV, visible, and near-infrared illumination with selectable emission filters and a calibrated digital camera; the primary bench...
- Watermark
- A pattern formed in paper during manufacture by localised fibre-density variation on the Fourdrinier wire; visible in transmitted light as a lighter...
Explained in
- Detection Methods: Oblique, Transmitted, UV, IR and the VSCIllumination of a document surface at a very low angle (5-20 degrees) to create disproportionately long shadows from surface irregularities, revealing mechanic...